<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Any chemical compound, biological object, physical factor in a concentration or amount that adversely alters the physical, chemical, or biological properties of the environment. The term includes pathogens, toxic metals, carcinogens, oxygen-demanding materials, radiation, natural substances, synthetic industrial chemicals, biocides and all other harmful substances and factors. (NCI)</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>